Process for recovery of metals from alloys and metallurgical residues



May 7, 1940.`

C. WHITE PROCESS FOR RECOVERY OF METALS FROM ALLOYS AND METALLURIGAL RESIDUS Filed Feb. 1, 1939 N. @am @Mulan wml Q abre/mm3 Patented May 7, 1940 UNITED STATES PATENT OFFICE PROCESS FOR RECOVERY OF METALS FROM ALLOYS AND METALLURGICAL RESIDUES 1 Claim.

'I'his invention relates to the separation of metals from scrap material, metallurgical byproducts and comercial residues containing copper, lead, tin, zinc, iron, nickel, antimony,

5 silver, etc., and the recovery of electrolytic copper and lead.

One of the objects of my invention is to provide a method of obtaining pure copper electrolytically from a foul solution containing substantial quantities of zinc, nickel, iron, etc. Another object is to recover and regenerate the spent electrolyte in order to provide a continuous cyclic process. These and other objects will appear from the following description taken in connection with the accompanying drawing which is a schematic illustration of apparatus for practicing my process.

'I'he brass, bronze and other alloy materials may be first reduced in a blast or smelting furnace to separate the metals from the non-metallic contents and the molten metal is then cast directly into the form of anode plates suitable for deposition in the electrolytic tanks.

The cast alloy anodes A with a corresponding l number of thin j sheet copper cathodes C, are suspended in a tank I, containing an electrolyte of an acid solution of copper nitrate. 'Ihe copper nitrate is derived by passing a spray of nitric acid through a mass of copper scrap or shot 5, in leaching tower 6, the electrolyte being iirst heated in a container l.

Under favorable conditions the copper, lead, iron, nickel and most of the zinc dissolvefin the acid electrolyte; while the tin, antimony, silver and a portion of the zinc, do not go into solution but form a sludge, which either adheres to the `anodes or settles to the bottom of the tank and is cleaned off periodically.

As is well known successful electrolysis is de- 40 pendent upon a constant supply of ions at the cathode. When a soluble anode is employed,

ions are supplied at the anode by the solution of the copper and thereby very greatly reduces the voltage required to plate the copper upon the cathode. Best results are obtained with a current of from .20 to .30 volts per plate and a current density of from 12 to 18 amperes per square foot of cathode surface although satisfactory results may be obtained with other current 0 densities. Moreover the continuous replenish'- ment of the copper nitrate by the dissolving copper does not interfere with the efficient operation of the electrolytic action, whereas when a copper sulphate electrolyte is employed, the solution in 55 the immediate vicinity of the anode isy always supersaturated as the copper dissolves and copper sulphate will crystallize on the electrode if the acid content is too high, thereby rendering the anode less soluble, with the consequent cutting down of the copper content of the electrolyte and an increase in the voltage required.

Under proper conditions I obtain copper cathodes of 99.97 to 99.99 per cent purity. Favorable conditions exist with an electrolyte of acidity registered by pH from ,1 to 2 at a tem- 10 perature of 40 to 55 C., with a content of 30 to 40 grams oi copper per liter andan electrolyte circulation of 4 gallons per tank per minute. Other combinations of temperature, acidity and copper content can be employed satisfactorily. l5

When the lead content of the electrolyte in tank I builds up to a worthwhile concentration, as for example, from 10 to 15 grams per liter, the solution is allowed to pass into a tank 2, which is provided with thin sheet copper cathodes C and insoluble anodes I, such as platinum, carbon etc. By electrolytic action in this tank, the lead is recovered at the'anode as pure lead peroxide PbOz, while copper from the electrolyte is deposited upon the cathode with some regenerayi tion of acid. The electrolytic solution is then pumped from tank 2 to the spray head I0 oi the uppermost section of the condenserl I2.

When the solution in tank I builds up with zinc, nickel, iron and other impurities to an ex- 30 tent that might interfere with the emciency of the electrolytic process, it is transferred to tank 3 having insoluble anodes I and thin sheet copper cathodes C2, in which the lead and copper content are completely removed electrolytically. The 35 resulting solution is transferred to a still Il in which it is heated to break up the nitrates. 'I'he nitric acid together with any oxides of nitrogen are collected in the condenser I2. The residue contains oxides of zinc, nickel, iron, etc. which o can be treated by the usual metallurgical processes to recover the Zinc and nickel.

'I'he oxides of nitrogen from the evaporator I4 together with the oxides of nitrogen and air supply from the leaching tower 6 pass into the lowest scrubbing section of the condenser I2 and percolate upwardly through the mass of broken stone I3 or other suitable rubble inert to nitric acid, such as quartz, rock or chemical stoneware, to combine with the spent electrolyte entering through the spray heads I0 in the upper part of each condenser section and thereby regenerate the supply of nitric acid.

The recycling of the spent electrolyte in countercurrent relationship to the iiow of the gaseous i oxides of nitrogen, provides a continuous cyclic renewal of the nitric acid solvent. This feature of the method is of great importance and is a vital factor in the practical recovery of metals from scrap metal and metallurgical by-products by means of nitric acid solvents on a commercial scale.

By the process disclosed herein, copper of the highest purity may be obtained electrolytically, directly from unrened commercial scrap metal and is deposited from a foul electrolyte. Whereas the quality of the electroly'tic copper produced by the leading reneries runs about 99.96% pure, I am enabled to obtain copper of 99.97 to 99.99 per cent purity by the process described herein. It will be appreciated by metallurgists that this small improvement in quality is important. Flirthermore spectrographic tests of copper obtained by my method show less and fewer impurities than electrolytic copper made by the sulphate process. Also, as pointed out above, my present process requires less current to maintain a constant supply of ions at the cathode during the electrolytic process.

I claim:

'I'he method of treating materials such as scrap metal, brass, commercial residues and metallurgical by-products, containing copper in major amount and metals such as, tin, lead, zinc, nickel and silver in minor amount to separate and recover said individual metals, which com.- prises melting said materials and casting the molten metal into the. form of anodes, utilizing said anodes with cathodes of copper or other suitable material in an electrolyzing tank lcontaining an electrolyte consisting essentially of a nitric acid solution of copper nitrate passing an electric current between the anodes and cathodes to dissolve the copper, lead, zinc, iron and nickel from the anodes, the tin and silver separating from the anodes as a sludge, and to deposit only substantially pure copper upon saidcathoydes.

CLARENCE B. WHITE. 

